The present invention relates to process chambers for processing substrates in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to an electron filter for removing dissociated electrons from a process chamber, particularly an ion implantation chamber for semiconductors.
Generally, the process for manufacturing integrated circuits on a silicon wafer substrate typically involves deposition of a thin dielectric or conductive film on the wafer using oxidation or any of a variety of chemical vapor deposition processes; formation of a circuit pattern on a layer of photoresist material by photolithography; placing a photoresist mask layer corresponding to the circuit pattern on the wafer; etching of the circuit pattern in the conductive layer on the wafer; and stripping of the photoresist mask layer from the wafer. Each of these steps, particularly the photoresist stripping step, provides abundant opportunity for organic, metal and other potential circuit-contaminating particles to accumulate on the wafer surface.
In the semiconductor fabrication industry, minimization of particle contamination on semiconductor wafers increases in importance as the integrated circuit devices on the wafers decrease in size. With the reduced size of the devices, a contaminant having a particular size occupies a relatively larger percentage of the available space for circuit elements on the wafer as compared to wafers containing the larger devices of the past. Moreover, the presence of particles in the integrated circuits compromises the functional integrity of the devices in the finished electronic product. Currently, mini-environment based IC manufacturing facilities are equipped to control airborne particles much smaller than 1.0 xcexcm, as surface contamination continues to be of high priority to semiconductor manufacturers. To achieve an ultra-clean wafer surface, particles must be removed from the wafer, and particle-removing methods are therefore of utmost importance in the fabrication of semiconductors.
Ion implantation is a processing step commonly used in the fabrication of the integrated circuits on the wafer. Ion implantation is a form of doping, in which a substance is embedded into the crystal structure of the semiconductor substrate to modify the electronic properties of the substrate. Ion implantation is a physical process which involves driving high-energy ions into the substrate using a high-voltage ion bombardment. The process usually follows the photolithography step in the fabrication of the circuits on the wafer.
The ion implantation process is carried out in an ion implanter, which generates positively-charged dopant ions in a source material. A mass analyzer separates the ions from the source material to form a beam of the dopant ions, which is accelerated to a high velocity by a voltage field. The kinetic energy attained by the accelerated ions enables the ions to collide with and become embedded in the silicon crystal structure of the, substrate. Finally, the doped silicon substrate is subjected to a thermal anneal step to activate the dopant ions.
A typical conventional ion implantation chamber is generally indicated by reference numeral 10 in FIG. 1 and includes a chamber wall 12 that is provided with a chamber bottom 13 and defines a chamber interior 14. A chamber lid 16 may be provided for closing the chamber interior 14. A scan wheel 18, having a rotatable hub 19 from which extend multiple spoke arms 20, is mounted in the chamber interior 14. A wafer holder 21 is mounted on the extending end of each spoke arm 20. In application, a wafer 22 is mounted on the bottom surface of each wafer holder 21 for the implantation of ions in the wafer 22, as shown in FIG. 2. An ion beam generating system 24, disposed beneath the chamber bottom 13, generates and emits an ion beam 25 upwardly through an elongated slot 15 provided in the chamber bottom 13 adjacent to the scan wheel 18. Accordingly, as the scan wheel 18 rotates typically at a speed of about 900 r.p.m., as indicated in FIG. 1, the wafers 22 mounted on the bottom surfaces of the respective wafer holders 21 are passed over the slot 15, such that the ion beam 25 strikes the surface of the wafer 22 and implants ions from the ion beam 25 into the material layer or layers (not shown) on the wafer 22. A cryo pump 27 is operated to draw process gases and other residual chemicals from the chamber interior 14, through a pump opening 28 in the chamber bottom 13.
The ion implantation process heretofore described is carried out under high-vacuum conditions in the chamber interior 18. These conditions produce dissociated electrons, which adhere to the surface of the wafer 22 during and after the process and are a major source of particle contamination. The resulting particle contamination adversely affects the yield of devices having features with sizes less than 0.13 xcexcm on the wafer 22.
Accordingly, an object of the present invention is to provide an electron filter for a process chamber used in the processing of substrates.
Another object of the present invention is to provide an electron filter for preventing or minimizing particle contamination of a substrate during or after an ion implantation process.
Still another object of the present invention is to provide an electron filter for trapping electrons during an ion implantation process.
Another object of the present invention is to provide an electron filter which contributes to a clean, reduced-particle environment inside a process chamber.
Yet another object of the present invention is to provide an electron filter which enhances the yield of devices on a substrate.
A still further object of the present invention is to provide an electron filter which is positively charged to facilitate trapping electrons during an ion implantation process.
Yet another object of the present invention is to provide an electron filter which may be used in conjunction with a cryo pump to remove dissociated electrons from the surfaces of substrates and trap the electrons to prevent or reduce particle contamination of the substrates.
Another object of the present invention is to provide a method of removing electrons from substrates or a process chamber in which substrates are processed in order to prevent or at least reduce particle contamination of the substrates.
Still another object of the present invention is to provide an ion implantation chamber which is equipped with an electron filter for the removal of electrons from substrates processed in the chamber or from the chamber interior.
In accordance with these and other objects and advantages, the present invention comprises an electron filter for trapping dissociated electrons in a substrate processing chamber. The electron filter typically includes at least one filter element which is connected to a voltage source for applying a positive voltage to the filter element. During an ion implantation process, dissociated electrons are drawn from the interior of the chamber and trapped in the filter element to prevent or reduce contamination of the substrates.
In a typical embodiment, the electron filter is mounted directly above a pump opening in the chamber bottom and electrons are trapped in the filter as a cryo pump evacuates particulate contaminants from the chamber. The electron filter may include upper and lower or upper, middle and lower filter elements separated from each other with spacers. In a typical embodiment, the filter element or elements typically have mesh openings less than about 1 mm wide.